1. Field of the Invention
This invention relates to a projection type image display apparatus for resolving illuminating light from an illuminating optical system into a plurality of color lights, combining the color lights modulated by an image display element and projecting and displaying an image.
2. Description of Related Art
There has heretofore been used a projection type image display apparatus for enlarging and projecting image light from an image display element by the use of an illuminating optical system for illuminating the image display element, and an image display element such as a liquid crystal display for modulating the polarized state of illuminating light and producing image light.
Image display apparatuses using a so-called reflection type image display element in which a side on which illuminating light from an illuminating optical system enters the image display element and a side on which image light modulated by the image display element emerges from the image display element are the same are proposed in Japanese Patent Application Laid-Open No. 10-274810, Japanese Patent Application Laid-Open No. 10-319344, etc.
The construction of the projection type image display apparatus of Japanese Patent Application Laid-Open No. 10-319344 is shown in FIG. 10 of the accompanying drawings. In this figure, the reference numeral 101 designates a light source, the reference numeral 102 denotes a reflector, the reference numeral 103 designates a filter, and the reference numerals 104 and 106 denote fly-eye lenses. Also, the reference numeral 105 designates a mirror, the reference numeral 107 denotes a polarizing beam splitter, the reference numeral 108 designates a color separating and synthesizing prism, the reference characters 109r, 109g and 109b denote image display elements, and the reference numeral 110 designates a projection lens.
The optical path IL of an illuminating optical system and the optical path PL of a projection optical system are combined together by the polarizing beam splitter 107 so as to pass through the single color separating and synthesizing prism 108.
However, the polarizing beam splitter for combining the optical paths together is comprised of multi-layer film and therefore, if the angle of light incident on the multi-layer film becomes irregular and departs from a design angle (e.g. 45°), there will arise the problem that the efficiency of separating the light into a P-polarized component and an S-polarized component is fluctuated and the loss of light occurs so that the image display apparatus becomes capable of projecting only a dark image.
Also, dichroic film in the color separating and synthesizing prism has its characteristic fluctuated by the angle of incidence. When light (illuminating light) entering the image display element enters as a beam having a predetermined expanse, there arises the problem that the unevenness of the incident angle conforming to the angle of expanse of the beam occurs in the dichroic film, whereby other color component than a predetermined color component mixes with the illuminating light to thereby reduce the color purity of the illuminating light.